Investigators began their probe into North Korea after they discovered similarities in the code used in the theft and the code used in the hacking attack on Sony Pictures in December 2014, CBS News senior investigative producer Pat Milton reports.

The Attack on Sony

The source said no firm evidence linking North Korea to the bank heist has been established and no charges have been brought yet.

The theft is considered to be one of the biggest bank robberies in modern times.

In the theft, the hackers, apparently using a global payment messaging system known as Swift, were able to cause the Federal Reserve Bank of New York to release money from the Bangladeshi bank’s accounts.

Most of the requests were rejected by officials after they apparently noticed irregularities, but a reported $81 million was released.